2816 Inorganic Chemistry, Vol. 13, No. 12, 1974
Gregory 9. Kubas and Llewellyn H. Jones Contribution from the University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87544
stants of the Tetracymide Ions of Nic GREGORY J. KUBAS and LLEWELLYN H. JONES* Received March 21, 1974
AIC40 192L
The complexes M(CN)42-,M(I3CN),'- [94% "C], and hf(C'SN)42-[99% "N], with M = Ni, Pd, and Pt, have been prepared. From Raman studies of aqueous solutions and infrared studies of aqueous solutions and solid powders, many of the vibrational frequencies have been determined. With certain judicious constraints included, force constants for a general quadratic force field have been estimated. The results indicate that for Pt(CN),'- the Pt-C u bond and Pt-CN "back" n bond are both stronger than for the other two metals.
Some time ago estimates of the potential constants of Pt(CN),'and PJi(CN)42- were made from analysis of vibrational spectra. No isotope shifts were available so it was necessary to make a number of constraints in the general quadratic force field. Since that time more unique force fields have been for several cyanide complexes using the additional data from the vibrational frequencies of species enriched in 13C and species enriched in "N. This paper is to report a study of the potential constants of Ni(CN),'-, Pd(CN),'-, and R(CN)42- from the vibrational spectra of the normal species, the completely substituted 13C species, and the completely substituted 15N species. Experimental Section Potassium cyanide enriched to 94% in I 3 C was prepared from "CH, and NH, by the method of Baufl, et ai., as modified by Goldblatt and Swanson.8 Similarly potassium cyanide enriched to 99% in "N was prepared from CH, and "NH,. We are grateful to W. J. McCreary of this laboratory for supplying us with 13CH, and to M. Alei of this laboratory for supplying us with "NH,. Preparation of Complexes. The normal and isotopically enriched (94% in I 3 C or 99% in "W) tetracyanometalates K,M('2C14N),, ICzM(13C14N),, and KzM(1ZC'5N)4were prepared b y dissolving the metal dicyanide in aqueous potassium cyanide, for M = Ni, Pd. Typically, aqueous solutions of metal dichloride (I mmol) and K'ZC14N, KI3C*"N,or K'2C'SN (2 mmol) were mixed and the resulting precipitate of metal dicyanide was filtered off and allowed to react with 2 mmol of the appropriate KCN species in 3 ml of water. The volume of the solution was reduced to 1 ml by careful evaporation on a hot plate, 4 ml of absolute ethanol was slowly added, and the mixture was cooled to 0'. Fine, needlelike crystals of the tetracyanometalate formed and were filtered off and washed with ethanol. The nickel salts were anhydrous and the palladium analogs were found to be monohydrates. The tetracyanoplatinites were prepared by fractional crystallization of an aqueous solution formed by mixing K,PtCl, (1 mmol) and KCN (4 mmol) in a minimum quantity of water. The tetracyanoplatinites are much less soluble at 0" than KCl and are readily crystallized and isolated as trihydrates. Two crystallizations were necessary to give a pure product. Recording of Spectra. Rainan spectra of the aqueous tetracyanometalates were recorded o n a Cary Model 82 equipped with Coherent Radiation Model 52 argon and krypton lasers. A Perkin-Elmer 521 was used to obtain infrared spectra of Nujol mulls of K,M(CN), species in the 4000-25O-~m-~ region and of aqueous solutions in the CN stretch region. To observe the combinations of CN stretches in the 4000-7000-cm-l region, a Cary Model 14 was used to record (1) This work was performed under t h e auspices of t h e U. S . Atomic Energy Commission. (2) D. M. Sweeny, I . Nakagawa, S . Mizushima, and J . V. Quagliano,J. Amer. Chenz. Soc., 78, 889 (1956). (3) R. L. McCullough, L. H. Jones, and G. A. Crosby, Spectro. chim. Acta, 16, 929 (1960). (4) L. H. Jones, J. Chem. Phys., 43, 594 (1965). (5) L. H. Jones,J. Chem. Phys., 44, 3643 (1965). (6) L. H. Jones, M. N. Memering, and R . I. Swanson, J . Chem. Phys., 54, 4666 (1971). (7)D. Baufl, S. Mlinko, and T. Palagyi, J. Lubel. Compounds, 7 , 221 (1971). (8) M. Goldblatt and B. I. Swanson, unpublished work in this laboratory.
spectra of samples dissolved in D,O which reduces the solvent absorption in this region.
Assignment of Frequencies The observed frequencies are listed in Tables I and 11. The M(CN)42- ions p o s ~ e s s Dsymmetry ~~ and, thus, will have 16 fundamental vibrations (2 Al,, 1 AZg,2 Blg, 2 BZg, 1 E,, 2 Azu, 2 B2,, and 4 E,). Of these, A2, and E, are infrared active only, while Alg, Big, BZg,and E, are Raman active only. The A2, and Bzu vibrations are inactive. The numerical ordering of frequencies is the same as that used earlier?s3 No B2, modes were observed. A l g . The AI, CN and MC stretches, v 1 and v 2 ,are readily assigned from polarization data (Table I). Big. The B1, CN stretching vibration, v4, is observed as a depolarized Raman frequency (Table I). The B1, hIC stretching vibration is obscured by the Alg MC stretch. However, it is brought out when the Al, mode is eliminated by z(xz)y polarization. This is analogous to the cases of Au(CN)
